docs: def before_export(self):
          """
          Set the attributes nbytes
          """
          # sanity check that eff_ruptures have been set, i.e. are not -1
          try:
              csm_info = self.datastore['csm_info']
          except KeyError:
              csm_info = self.datastore['csm_info'] = self.csm.info
          for sm in csm_info.source_models:
              for sg in sm.src_groups:
                  assert sg.eff_ruptures != -1, sg
  
          for key in self.datastore:
              self.datastore.set_nbytes(key)
          self.datastore.flush()